1. Field of the Invention
The invention relates to a microelectromechanical system (MEMS) device.
2. Description of Related Art
Along with the development of the technology, a mechanical device may be made smaller. For example, a tiny mechanical device, e.g. a MEMS device, may be manufactured by semiconductor processes, and the MEMS device may be driven by electricity. As a result, an apparatus or device, e.g. an electronic device, including the MEMS device may be made smaller or achieve more or better functions by using a large amount of the MEMS units.
A digital micro-mirror device (DMD) is a kind of MEMS device and has a plurality of micro-mirrors arranged in an array and driven by electricity. The DMD may serve as a reflective display panel. Compared with a liquid crystal display panel which has a liquid crystal layer and polarizer that cause great light loss, the DMD has micro-mirrors with high reflectivity so as to achieve high light efficiency.
In the DMD, the swing of the micro-mirrors is driven by electrostatic force. When a micro-mirror swings to an on state, the micro-mirror reflects light from the illumination system to a projection lens. When the micro-mirror swings to an off state, the micro-mirror reflects light to a direction deviating from the projection lens. The ratio of the period of the on state to the period of the off state of a micro-mirror determines a gray level of a pixel in a frame. How to effectively use the electrostatic force to switch the state of the micro-mirror and how to improve the lifetime of the DMD are important for achieving a display with high reliability, a wide operation window, and long lifetime.